1. Field of the Invention
The present invention relates to a semiconductor package and a method for manufacturing the same.
2. Description of the Related Art
Presently, semiconductor devices such as an insulated gate bipolar transistor (IGBT) and an injection enhanced gate transistor (IEGT), and a metal oxide semiconductor field effect transistor (MOSFET) are being used as a power semiconductor device. The semiconductor device is formed in a sheet-like shape. The semiconductor device includes an upper surface side power terminal and a control terminal on its upper surface. It also has a back surface side power terminal on its back surface side.
Note that if the semiconductor device is an IGBT device, the upper surface side power terminal is an emitter electrode, the back surface side power terminal is a collector electrode, and the control terminal is a gate electrode.
To mount such a semiconductor device onto a substrate so as to provide a semiconductor package, the back surface side power terminal of the semiconductor device is connected to an electrode on the upper surface side of the substrate by solder jointing as described in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 2002-164485 and 2003-110064. Further, the upper surface side power terminal and the control terminal of the semiconductor device are connected to electrodes on the upper surface side of the substrate by wire bonding using an aluminum wire.
However, in the case of using wire bonding to connect a semiconductor device and substrate electrodes, wires are bonded one at a time, and so the bonding process takes time. It may thus lead to an increase in manufacturing cost for connection between a semiconductor device and electrodes. In the wire bonding, the wire has a loop-like form, thus has a long wire length, which fact may bring about an increase in inductance of interconnections and outer size of the device. Moreover, if vibration applied to the semiconductor device, there is a possibility that the wire may be disconnected or come in contact with an adjacent wire, etc., thus leading to a short-circuit.
To solve those problems, in place of the method of bonding a wire to the upper surface side power terminal of a semiconductor device, such a method is being used as to bond an aluminum thin plate, etc., or join a flat plate or a lead by soldering and lead it out as an electrode.
In a semiconductor module including a plurality of such the semiconductor devices, such the semiconductor packages are arranged in line on a substrate, which acts as a radiator plate. In this case, the back surface of the semiconductor package is jointed onto the substrate. This semiconductor module is installed in a power control device such as an inverter or a converter.
In this semiconductor module, only one surface of each of the semiconductor packages is in contact with the substrate, so that heat cannot be radiated sufficiently. Further, due to the constitution in which the back surface of the plate of each semiconductor package is jointed onto the substrate, an area in which the semiconductor packages are installed becomes large with respect to the area of the substrate. That is, it may lead to an increase in size of the semiconductor module.
To prevent those, according to a known method, first the semiconductor packages are arranged in a line. Next, those semiconductor packages are sandwiched vertically between a pair of conductive members such as bus bars, and are installed on the substrate.
However, the pair of conductive members have thermal conductivity and so such members also act as heat-radiation members. Therefore, the conductive members thermally expand as they are supplied with a current and then contract. In addition, the end of the conductor member on the side of the substrate is fixed and the other end thereof is free. Accordingly, the conductor member thermally expands and contracts differently between the free end and the fixed end thereof. In particular, the conductive member thermally expands and contracts at its free end greater than it does at the other end. This behavior may apply an external force on the semiconductor packages, thus damaging them.
Further, in order to reduce the size of the semiconductor package, the connection portion of each of the terminals of the semiconductor device must also be reduced in size. Therefore, in the method of manufacturing the semiconductor packages, they cannot be jointed satisfactorily in some cases. This may easily cause damage to the jointing portions.
To prevent such damage, such a method is available as to increase the jointing area or joint not only one surface but also the side surfaces consistently by using solder (or adhesive agent etc.) for the purpose of sufficient jointing. However, such method may lead to an increase in number of soldering positions and also in number of assembly processes such as processes of soldering, installing of spacers, and welding, etc. Such an increase in the number of the assembly processes may bring about an increase in mass production costs.